Thyrotropin-releasing hormone (TRH) selectively and rapidly stimulates phosphatidylinositol turnover in GH pituitary cells: a possible second step of TRH action.
TRH was found to rapidly influence 32PO4 incorporation into phospholipids of PRL-secreting GH pituitary cells. Analogs of TRH were found to exert similar effects, with potencies related to receptor-binding affinity. Additional PRL-releasing agents were also tested. Bombesin exerted a similar effect, whereas vasoactive intestinal polypeptide, 8-bromo cAMP, phosphodiesterase inhibitors, 50 mM K+, and scorpion venom toxin had no influence. Cationophore A23187 stimulated phospholipid labeling in a manner distinguishable from that of TRH. Chromatographic analysis showed the action of TRH to be restricted to the labeling of phosphatidylinositol and phosphatidic acid. Kinetic studies indicated a rapid influence of TRH on phosphatidylinositol breakdown, with subsequent accelerated 32PO4 incorporation into phosphatidylinositol and phosphatidic acid. These studied identified a rapid, receptor-mediated, cAMP-independent action of TRH on phospholipid metabolism. Similar effects of other hormones are believed to be involved in promoting cellular Ca2+ translocation. The rapid onset of the response reported here suggests that this event may play a role in mediating the PRL-releasing effects of TRH and bombesin in GH cells.
D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002460:Cell Line; D007700:Kinetics; D010710:Phosphates / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology*
D010710:Phosphates; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D000001:Calcimycin; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D001839:Bombesin